1. Field of the Invention
This invention relates to new polyamides which are suitable for use as adhesives, particularly hotmelt adhesives. The new polyamide resins contain dimerized fatty acids on the acid side condensed with polyoxyalkylene urea diamines capable of diamide formation on the base side.
2. Statement of Related Art
Hotmelt adhesives are acquiring increasing significance in numerous areas of bonding technology. The advantages of hotmelts lie in the fact that they develop the necessary bond strength by cooling from the melt and, accordingly, are suitable for high-speed production processes. Further advantages lie in the fact that there is no need for apparatus for protection against solvent vapors and the often long drying times required for water-based adhesives are avoided.
One important class of hotmelt adhesives are the polyamides, among which polyamides based on dimerized fatty acids have acquired particular significance. Among the polyamides based on dimerized fatty acids, polyamides which contain dimerized fatty acids in the acid component and ether diamines in the amine component are particularly preferred by virtue of their good low-temperature properties.
German Patent document DE-A 27 54 233 describes copolyamide resins which, on the acid side, contain a special mixture of polymeric fatty acids (dimer fatty acid) and aliphatic C.sub.6 -C.sub.12 dicarboxylic acids and, on the base side, a mixture of saturated aliphatic diamines and polyoxyalkylenediamines. The products show a brittleness temperature of -25.degree. C.
Similar resins are described in U.S. Pat. No. 4,218,351 which relates to polyamides containing 5 to 50 mol-% dimer fatty acid and 0.25 to 12.5 mol-% amorphous oligomers (polyoxyalkylene diamines) in addition to standard raw materials. Although the behavior of the composition at very low temperatures can be improved as disclosed in the patent, an additional mixing step is necessary.
Although the polyether diamine-containing polyamides mentioned above show satisfactory properties for many applications, it was nevertheless desirable to improve their behavior at low temperatures and their adhesion to various substrates.
Accordingly, an object of the present invention is to provide improved polyamides which may be used as hotmelt adhesives.
Yet another object of this invention is to provide polyamides having improved low temperature flexibility.